Rotary kiln heat exchanger and method of assembling same

ABSTRACT

Rotary kiln heal exchangers having precast hub and leg assemblies are disclosed. The hub and leg assemblies include interlocking features which secure the heat exchanger components together. A method of installing such heat exchangers in rotary kilns is also disclosed. Installation is relatively fast and simple, and the heat exchangers are capable of withstanding the harsh operating conditions of rotary kilns for extended periods of time.

CROSS-REFERENCES TO RELATED APPLICATIONS

More than one reissue application has been filed for the reissue of U.S.Pat. No. 6,688,884 B2. The reissue applications are application Ser. No.11/069,643 and application Ser. No. 12/152,878 (the presentapplication), which is a divisional reissue of Reissue application Ser.No. 11/069,643.

FIELD OF THE INVENTION

This invention relates to rotary kilns, and more particularly relates toheat exchangers installed in rotary kilns.

BACKGROUND INFORMATION

Rotary kilns are long, slightly inclined cylinders used for processingmaterials such as lime, limestone, dolomite, magnesite, petroleum cokeand cement. The material to be treated is introduced at the higher endand heated air flowing counter-current to the material is introduced atthe lower end. Rotary kilns generally operate on a twenty-four hourbasis for several months between scheduled down periods.

Rotary kilns typically have a refractory brick interior and a steelshell exterior, and some have at least one heat exchanger. The heatexchanger divides the cross section of the kiln into three or moresegments to enhance the heat transfer from the gas to the material andimprove mixing of the material. A three-segment heat exchanger comprisesthree spokes or legs which extend from the axial center of the kiln tolocations equally spaced around the interior circumference of the steelshell. Commercially available three-segment heat exchangers have beensold under the trademark Trefoil®.

Rotary kiln heat exchangers encounter harsh operating conditions. Forexample, internal gas temperatures may typically be 1,000 to 3,000° F.in a highly basic atmosphere in a rotary lime kiln, althoughtemperatures outside of this range are possible depending on theparticular application. The heat exchanger must take the structuralloading and erosion, e.g., from several hundred tons per day ofpartially calcined rock that slides across or falls against the surfacesof the heat exchanger. Furthermore, the heat exchanger rotatescontinuously with the kiln, which subjects the components of the heatexchanger to varying compressive and tensile forces. The heat exchangermust also withstand the kiln shell deflection upon revolution over itsroller supports.

Conventional rotary kiln heat exchangers are typically from 8 to 16 feetlong along the longitudinal kiln axis, depending on the kiln diameterand other parameters, and have spokes or legs typically from 9 to 13.5inches thick. The heat exchangers are usually formed from individualrefractory bricks, although some have been formed in-situ fromrefractory materials which are cast and cured inside the kiln.Installation of conventional brick heat exchangers is labor-intensiveand requires specially skilled artisans. The bricks also requirecomplicated forms specific to a single rotary kiln size to support themduring construction. Thus, brick heat exchangers are slow to install andare expensive. In-situ cast refractory heat exchangers also suffer fromdisadvantages such as premature wear, complicated forms and slowerinstallation than brick.

Some examples of rotary kiln heat exchanger designs are disclosed inU.S. Pat. No. 3,030,091 to Wicken et al., U.S. Pat. No. 3,036,822 toAndersen, U.S. Pat. No. 3,169,016 to Wicken et al., U.S. Pat. No.3,175,815 to Wicken et al., U.S. Pat. No. 4,846,677 to Crivelli et al,U.S. Pat. No. 5,330,351 to Ransom et al. and U.S. Pat. No. 6,257,878 toMarr et al.

Despite these prior designs, a need still exists for a rotary kiln heatexchanger that is relatively fast and simple to install, and canwithstand the harsh operating conditions of rotary kilns for extendedperiods of time. The present invention has been developed in view of theforegoing, and to address other deficiencies of the prior art.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide a precast monolithicrotary kiln heat exchanger hub comprising at least one recessed surfaceconfigured for engagement with a heat exchanger leg.

Another aspect of the present invention is to provide a rotary kiln heatexchanger hub comprising at least one portion configured forinterlocking engagement with a heat exchanger leg, and at least oneportion configured for slidable engagement with another heat exchangerleg.

A further aspect of the present invention is to provide a rotary kilnheat exchanger assembly comprising a heat exchanger hub includingrecesses, and heat exchanger legs received in the heat exchanger hubrecesses.

Another aspect of the present invention is to provide a rotary kiln heatexchanger assembly comprising a heat exchanger hub, at least one precastheat exchanger leg interlocked with the trefoil hub, and at feast oneprecast heat exchanger leg slidably mounted in the trefoil hub.

A further aspect of the present invention is to provide a precast rotarykiln heat exchanger leg comprising an end configured for engagement witha heat exchanger hub.

Another aspect of the present invention is to provide a precast rotarykiln heat exchanger leg comprising a recess and/or protrusion extendingalong a side surface of the leg for engagement with a protrusion and/orrecess of an adjacent heat exchanger leg.

A further aspect of the present invention is to provide a precast rotarykiln heat exchanger leg comprising an end including at least one recessor protrusion for engagement with an interior wall of a rotary kiln.

Another aspect of the present invention is to provide a precast rotarykiln heat exchanger leg comprising an end including means for adjustingthe radial location of the heat exchanger in a rotary kiln.

A further aspect of the present invention is to provide a precast rotarykiln heat exchanger leg comprising a flared end for installationadjacent to an interior wall of a rotary kiln.

Another aspect of the present invention is to provide a rotary kilncomprising a refractory lining in the kiln, and a heat exchangerassembly in the kiln including precast heat exchanger legs and a centralheat exchanger hub.

A further aspect of the present invention is to provide a rotary kilncomprising a refractory lining in the kiln, and a heat exchangerassembly in the kiln. The heat exchanger assembly includes a heatexchanger hub comprising recesses, and heat exchanger legs received inthe heat exchanger hub recesses.

Another aspect of the present invention is to provide a method ofinstalling a heat exchanger in a rotary kiln. The method comprises thesteps of providing precast heat exchanger legs, providing a precast heatexchanger hub, and assembling the precast heat exchanger legs andprecast heat exchanger hub in the rotary kiln.

A further aspect of the present invention is to provide a method ofinstalling a heat exchanger in a rotary kiln. The method comprisespositioning first and second heat exchanger legs in the kiln at initialpositions, installing a hub between the first and second legs by movingthe first and second legs from their initial positions to installedpositions in which the first and second legs are engaged with the hub,and installing a third heat exchanger leg by engaging the third heatexchanger leg with the hub.

These and other aspects of the present invention will be more apparentfrom the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view shown with parts broken away of aconventional rotary kiln having a three-chamber brick heat exchanger.

FIG. 2 is an enlarged cross sectional view thereof illustrating a heatexchanger installed in the kiln in accordance with an embodiment of thepresent invention.

FIG. 3 is a detached elevational view of a heat exchanger hub inaccordance with an embodiment of the present invention.

FIG. 4 is a right side view of the heat exchanger hub of FIG. 3.

FIG. 5 is a left side view of the heat exchanger hub of FIG. 3.

FIG. 6 is a bottom view of the heat exchanger hub of FIG. 3.

FIG. 7 is an elevational view of a heat exchanger leg in accordance withan embodiment of the present invention.

FIG. 8 is a right end view of the heat exchanger leg of FIG. 7.

FIG. 9 is a cross sectional view taken on section 9-9 of the heatexchanger leg shown in FIG. 7.

FIG. 10 is a top view of another heat exchanger leg in accordance withan embodiment of the present invention.

FIG. 11 is a right end view of the heat exchanger leg of FIG. 10.

FIG. 12 is an exploded isometric view illustrating the assembly of aheat exchanger hub and heat exchanger legs in accordance with anembodiment of the present invention.

FIG. 13 is a partial sectional view taken through section 13-13 of FIG.2, illustrating raised courses of bricks between a heat exchanger legand a refractory brick lining of a rotary kiln.

FIGS. 14-17 illustrate sequential steps for installing a heat exchangerin a rotary kiln shell in accordance with an embodiment of the presentinvention.

FIG. 17A is a view of a heat exchanger leg showing shims beneath theouter end thereof.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for the purposeof illustrating the preferred embodiment of the invention only, and notfor the purpose of limiting same, FIG. 1 shows a rotary kiln 10including a heat exchanger 30 according to the present invention. Therotary kiln 10 has a steel shell 32 which is shown broken away so thatthe heat exchanger 30 is fully shown. The rotary kiln 10 may be, forexample, 100 to 650 feet in length and 3 to 25 feet in diameter. Theheat exchanger 30 occupies a longitudinal section in the middle of thekiln 10. The heat exchanger 30 may be, e.g., from 8 to 30 feet inlength. Although not shown in FIG. 1, the rotary kiln 10 may containmore than one heat exchanger sections 30.

The rotary kiln 10 is mounted for rotation on trunions 16 with theinfluent end 18 elevated so that a charge of material to be processedcan flow by gravity downstream within the kiln as it rotates. The rotarykiln 10 at the effluent end 20 discharges the dried and/or calcinedmaterial. Heated air and gaseous products of combustion, indicated byarrows 22, are introduced at the effluent end 20 and flow in acountercurrent direction to the material being processed. Because theheat exchanger structure is subjected to extremely high torsional forcesfrom the flowing materials charged, various means of construction areused to minimize the effect thereof. A retainer ring 24 may beconstructed downstream from the heat exchanger 30. The retainer ring 24is secured adjacent to a brick lining 34. A shaped refractory bricklining 34 is installed in the kiln 10 between legs 50, 50a and 64 ofheat exchanger 30.

Referring now to FIG. 2, a rotary kiln heat exchanger 30 in accordancewith a preferred embodiment of the present invention is shown incross-section. The heat exchanger 30 is installed in rotary kiln shell32. Refractory brick lining 34 is installed inside the shell 32. Theheat exchanger 30 includes a heat exchanger hub 40 engaged with a firstheat exchanger leg 50, a second heat exchanger leg 50a, and a third heatexchanger leg 64. In the embodiment shown in FIG. 2, the inner ends ofthe legs 50, 50a, and 64 fit with an interlocking arrangement withinrecesses in the hub 40, as more fully described below.

FIGS. 3-6 illustrate details of the hub 40. As shown most clearly inFIG. 3, the hub 40 includes recessed portions 41. In this embodiment,the hub 40 includes three recesses 41 for receiving three heat exchangerlegs. Alternatively, the hub 40 could include a different number ofrecesses depending upon the number of heat exchanger legs that are used.

As shown in FIGS. 3-6, the recessed portions 41 of the hub 40 includeseveral protrusions 42 and recesses 43 which provide for interlockingengagement with the legs 50 and 50a, as more fully described below. Asshown most clearly in FIGS. 3 and 5, one of the hub recesses 41 includespin slots 46 which are arranged for alignment with corresponding pinslots in the leg 64, as more fully described below.

In the embodiment shown in FIGS. 3-6, the hub 40 may be formed of anyprecast monolithic refractory material having an alumina content of atleast 70% by composition, and more preferably, a refractory materialhaving an alumina content of about 80% to about 95% by composition. Inone embodiment, hub 40 is formed of a dense, low cement/high alumina(80-85%) castable. The refractory material may optionally be reinforcedwith materials such as metal fibers, e.g., stainless steel, such as byway of example and not limitation, 430ss, 310ss and/or 304ss. The lengthof the hub 40 may range from about 10 to about 24 inches, preferablyfrom about 12 to about 18 inches. The thickness of the arms of the hub40 may range from about 6 to about 15 inches, preferably from about 8 toabout 13.5 inches.

FIGS. 7-9 illustrate details of the leg 50. As shown in FIG. 7, the leg50 includes a relatively narrow mid-section 51, a flared inner end 52,and a flared outer end 53. The flared inner end 52 preferably has athickness at least 20 percent greater than the thickness of themid-section 51, more preferably from about 25 to about 40 percentgreater. The flared outer end 53 preferably has a thickness at least 40percent greater than the thickness of the mid-section 51, morepreferably from about 55 to about 65 percent greater. The mid-section 51may have a thickness of from about 6 to about 15 inches, preferably fromabout 8 to about 13.5 inches. The overall length “L” of the leg 50 mayrange from about 3 to about 8 feet, preferably from about 4 to about 6.5feet. The depth “D” of the leg 50 may range from about 8 to about 18inches, preferably from about 8 to about 12 inches.

As shown most clearly in FIGS. 7 and 9, the leg 50 includes a protrusion54 which runs along a portion of the length of the leg 50. A recess 55is provided on the opposite side of the leg 50. When multiple legs 50are stacked together along the axial length of the rotary kiln, theprotrusion 54 of one leg fits within the corresponding recess 55 of theadjacent leg. In this manner, the adjacent leg sections may beinterlocked.

As shown most clearly in FIGS. 7 and 8, the inner end 52 of the leg 50includes an extended tip 56. The extended tip 56 fits within one of therecesses 41 of the hub 40. Protrusions 57 and recesses 58 are providedat the inner end 52 of the leg 50. In accordance with a preferredembodiment of the present invention, the protrusions 57 and recesses 58provide for interlocking engagement with the corresponding recesses 43and protrusions 42 of the hub 40.

As shown in FIG. 7, a channel 60 is provided at the outer end 53 of theleg 50. The channel may have any suitable dimensions, e.g., a depth offrom about 1.5 to about 3 inches, and a width of from about 3 to about 7inches. The outer end 53 of the leg includes a slot 61 that isdimensioned to receive a metal member, such as a bar, plate or channel(not shown) on the inner surface of the kiln shell to adjust and lock inplace the radial position of the leg 50 within the rotary kiln. As shownin FIG. 2, the channel 60 is shaped to receive a bar 70 runninglongitudinally along the inner surface of the rotary kiln shell. Thechannel 60 and bar 70 arrangement helps secure the leg 50 in the desiredlocation with respect to the shell 32. The bar 70 may be made of steelor the like, and is attached to the shell 32 by any suitable means suchas welding, mechanical fasteners, etc. Although a single bar 70 is shownin the embodiment of FIG. 2, multiple bars may alternatively be used. Inaddition to, or in place of, the bars 70 which run longitudinally alongthe inner surface of the shell 32, other bar configurations may be used,such as bars forming rings around the inner circumference of the shell32. Basically, any means that adequately secures the leg 50 in thedesired position against the interior of the shell 32 may be used.

FIGS. 10 and 11 illustrate details of the leg 64. Many of the featuresof the leg 64 are the same as the features of the leg 50. However, theinner end 52 of the leg 64 includes pin slots 66 instead of theprotrusions and recesses 57 and 58 of the leg 50. The pin slots 66 arearranged such that they line up with corresponding pin slots 46 of thehub 40. As more fully described below, such a pin slot arrangementfacilitates installation and securement of the leg 64 in relation to thehub 40.

The legs 50, 50a and 64 are preferably formed of a monolithic refractorymaterial having an alumina content of at least 70% by composition, andmore preferably, having an alumina content of about 80% to about 95% bycomposition. In one embodiment, legs 50, 50a and 64 are formed of adense, low cement/high alumina (80-85%) castable. The refractorymaterial may be reinforced with metal fibers, e.g., stainless steel,such as by way of example and not limitation, 430ss, 310ss and/or 304ssfibers.

FIG. 12 is an exploded isometric view illustrating the arrangement ofthe hub 40 and the legs 50, 50a , 64 and 64a. The leg protrusions 57 fitwithin the hub recesses 43. Similarly, the hub protrusions 42 fit withinthe leg recesses 58. In this manner, the legs 50 and 50a interlockinglyengage with their respective hub recesses 41.

As shown in FIG. 12, the extended tip 56 of the leg 64 fits within itscorresponding recess 41 of the hub 40. In the installed position, thepin slots 66, 66a of the leg 64 are aligned with the pin slots 46 of thehub 40. When the slots 66, 66a and 46 are aligned, pins 67 may beinserted in the slots in order to provide additional securement betweenthe leg 64 and hub 40. The pins 67 preferably have diameters of fromabout 1 to about 2 inches, and lengths of from about 2 to about 6inches. The pins 67 may be made of any suitable material such as Inconel600 series or stainless steel 300 series alloys.

As shown in the embodiment of FIG. 12, the hub 40 has a height which is50% greater than the height of each of the legs 50, 50a and 64. Whenmultiple hubs 40 are installed along the axial length of the rotarykiln, and multiple legs are installed along the length of the kiln, thedifference in height between the hubs and the legs results in anarrangement of two hubs for every three sets of legs. This interlockingstaggered arrangement provides additional structural integrity for theheat exchanger.

FIG. 13 is a sectional view taken through section 13-13 of FIG. 2,illustrating a series of heat exchanger legs 50 (shown in cross section)installed in the refractory brick lining 34. Two courses of raisedbricks 76 are installed on each side of the legs 50. Another course ofraised bricks 74 is installed between the first two courses of raisedbricks 76 and the refractory brick lining 34 on both sides of the legs50. The raised brick courses 74 and 76 are preferably staggered as shownin FIG. 13 in order to prevent materials being treated in the kiln frominfiltrating the joints between the bricks, and to reduce or eliminatefracturing of the bricks and legs. As shown most clearly in FIG. 2, thefirst raised brick course 76 is of greater height than the second raisedbrick course 74 which, in turn, is greater in height than the refractorybrick lining 34. The height of the first raised brick course 76 ispreferably from about 9 to about 15 inches, while the height of thesecond raised brick course 74 is preferably from about 7 to about 12inches. The height of the lining 34 preferably ranges from about 6 toabout 9 inches. The raised brick courses 74 and 76 provide additionalmaterial to support the legs 50, 50a and 64 in regions of high stressconcentration, thereby reducing or eliminating cracking of the legs.

FIGS. 14-17 illustrate sequential steps for installing a heat exchangerin the rotary kiln shell 32 in accordance with an embodiment of thepresent invention. As shown in FIG. 14, the first leg 50 is positionedin the shell 32 with its outer end 53 located at a four o'clock position81. The initial position of the leg 50 is designated as P₁ in FIG. 14.The axial center A of the rotary kiln shell 32 is shown in FIG. 14. Theinitial position P₁ of the first leg 50 is inclined at an angle,designated 85 in FIG. 14, with respect to the axial center A of theshell 32. FIG. 14 also illustrates an initial position P₁ of the secondleg 50a. The outer end 53 of the second leg 50a is located at an eighto'clock position 82 of the shell 32. In its initial position P₁, thesecond leg 50a is inclined at an angle, designated 86 in FIG. 14, withrespect to the center axis A of the shell 32. The angles 85 and 86preferably range from about 2 to about 8 degrees.

With the first and second legs 50 and 50a located at their respectiveinitial positions Pi, there is sufficient clearance between the legs forinsertion of the hub 40. The first and second legs 50 and 50a and thehub 40 may be moved from the positions shown in FIG. 14 to theinterlocking positions shown in FIG. 15. The first leg 50 is rotatedabout a point that substantially corresponds with the four o'clockposition 81. Similarly, the second leg 50a rotates about a pointsubstantially corresponding with the eight o'clock position 82. The hub40 is moved from the elevated position shown in FIG. 14 to the positionshown in FIG. 15, at which the center of the hub 40 substantiallycorresponds with the axial center A of the shell 32. The first andsecond legs 50 and 50a and the hub 40 are thus moved from their initialpositions as shown in FIG. 14 to their installed positions as shown inFIG. 15.

FIG. 16 illustrates the subsequent installation of the third leg 64 inthe shell 32. The outer end 53 of the third leg 64 is installed at thetwelve o'clock position 83 with respect to the shell 32. The inner end52 of the third leg 64 is slid into place against the hub 40. The pins67 (as shown in detail in FIG. 12) may be inserted between the third leg64 and hub 40 to thereby form an interlocking engagement between thethird leg 64 and the hub 40.

As will be appreciated by those skilled in the art, kiln shells are notperfectly cylindrical. Thus, when forming legs 50, 50a and 64, it willbe necessary to dimension such components to fit within the smallestcylindrical opening defined by the kiln shell. As a result, theinsertion of shims 92 between the outer ends of legs 50, 50a and 64 andkiln shell 32, may be required for one or many of such legs 50, 50a and64.

In one method of forming legs 50, 50a and 64, such legs are dimensionedshorter than necessary to fit within a given kiln shell, and the legsare then shimmed where necessary to account for areas of kiln shell 32that are out of round.

As shown in FIG. 17, after installation of the first, second and thirdlegs 50, 50a and 64, and the hub 40, the refractory brick lining 34 isinstalled against the shell 32, as well as the raised brick courses 74and 76.

The following example is intended to illustrate various aspects of thepresent invention, but is not intended to limit the scope of theinvention.

EXAMPLE

A heat exchanger is installed in a rotary kiln as follows. After theinternal surface of the kiln shell has been exposed and cleaned, thefollowing sequence is carried out.

-   -   1. enter kiln and establish a longitudinal centerline on the        lowest segment of radius, or 6 o'clock position;    -   2. measure interior circumference and divide circumference first        by one-half and record, then divide the circumference by thirds        and record;    -   3. from the first centerline on floor, measure one-half of the        circumference and establish upper point at the 12 o'clock        position. From this line measure back down shell both to the        left and right one-third of the circumference and establish        these centerlines, at approximately the 4 o'clock and 8 o'clock        positions;    -   4. at the 6 o'clock position, set track segments for the rolling        support table, the full length of work area;    -   5. set both monorail segments, approximately 20 degrees to the        left and 20 degrees to the right of the upper or 12 o'clock        position centerline;    -   6. establish the starting point of the heat exchanger and mark        kiln shell;    -   7. from each of the three centerlines, at 12 o'clock, 4 o'clock        and 8 o'clock positions, set the support channels and weld to        shell;    -   8. set one leg on the left side of a support table, and second        leg on the right side of the table, then raise table to up        position;    -   9. set a hub in place on the support table and lower these three        items into place;    -   10. with support table in the down position, set the remaining        leg into place and install locking pins; and    -   11. lower table, roll forward to next position and repeat steps        #8, #9 and #10.

This sequence is continued until the heat exchanger is completelyinstalled. Then the support table track and monorail segments areremoved and the remaining kiln brick lining is installed.

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

What is claimed is:
 1. A rotary kiln comprising: a refractory lining inthe kiln; and a heat exchanger assembly in the kiln including a heatexchanger hub comprising recesses, and heat exchanges legs received inthe heat exchanger hub recesses wherein the legs are installed adjacentto the refractory lining with at least one course of raised bricks.
 2. Arotary kiln comprising: a refractory lining in the kiln; and a heatexchanger assembly in the kiln including a heat exchanger hub comprisingrecesses, and heat exchanger legs received in the heat exchanger hubrecesses, wherein the legs are installed adjacent to the refractorylining with at least two courses of raised bricks, and the courses ofraised bricks have different heights.
 3. A method of installing a heatexchanger in a rotary kiln comprising: positioning first and second heatexchanger legs in the kiln at initial positions; installing a hubbetween the first and second legs by moving the first and second legsfrom their initial positions to installed positions in which the firstand second legs are engaged with the hub; and installing a third heatexchanger leg by engaging the third heat exchanger leg with the hub. 4.The method of claim 3, wherein the first and second heat exchanger legsare positioned at four o'clock and eight o'clock positions,respectively.
 5. The method of claim 3, wherein the third heat exchangerleg is installed at a twelve o'clock position.
 6. The method of claim 3,wherein at least one of said first and second heat exchanger legsincludes recesses and projections dimensioned to engage and interlockwith projections and recesses an said hub.
 7. The method of claim 6,wherein a third heat exchanger leg slides into position relative to saidhub.
 8. The method of claim 6 further comprising the step of insertingshims between said kiln and the outer end of at least one of said heatexchanger legs.
 9. The method of claim 3, wherein at least one of saidheat exchanger legs includes recesses and projections dimensioned toengage and interlock with projections and recesses on said hub, and atleast one of said heat exchanger legs is pinned to said hub.
 10. Atrefoil structure for a rotary kiln, said kiln having a cylindrical bodyhaving a metal shell and a refractory brick lining therewithin, saidtrefoil structure, comprising: a central hub comprised of a plurality ofside-by-side, pre-formed refractory hub sections, said hub sectionsaligned along a central axis that extends through said cylindrical body;and a plurality of legs extending radially outward from said hub to saidmetal shell, each of said legs comprised of side-by-side pre-formed legsections, each of said leg sections being a unitary cast refractoryshape that extends between said central hub and supports on said metalshell.
 11. A trefoil structure of claim 10, wherein said hub sectionsare axially thicker than said leg sections, wherein each hub sectionengages at least two side-by-side leg sections.
 12. A trefoil structureof claim 11, wherein shims are disposed between said metal shell and atleast one of said legs.
 13. A trefoil structure of claim 10, wherein theleg sections that form at least one of said legs are axially slidableinto engagement with said hub sections forming said hub.
 14. A trefoilstructure of claim 13, wherein said leg sections are pinned to said hubsections.
 15. A trefoil structure of claim 10, wherein at least one ofsaid legs is comprised of leg sections that have innermost ends thatinterlockingly engage with said hub sections, and at least one of saidlegs is comprised of leg sections that have innermost ends that slideaxially along the central axis of said cylindrical body into engagementwith said hub sections.
 16. A trefoil structure of claim 15, whereinsaid leg sections that slide into engagement with said hub sections arelocked in position by pins extending into aligned slots in saidslidably-aligned leg sections and said hub sections.
 17. A trefoilstructure of claim 15, wherein said leg sections that interlock withsaid hub sections have a plurality of recesses and protrusions formedalong said innermost end of said leg sections that mate with opposingprotrusions and recesses on said hub sections.
 18. A trefoil structurefor a rotary kiln, said kiln having a cylindrical body having a metalshell and a refractory brick lining therewithin, said trefoil structure,comprising: a refractory hub oriented along an axis that extends axiallythrough said cylindrical body; and a plurality of elongated leg sectionsthat extend radially from said hub to said metal shell, each of said legsections being an elongated cast refractory shape dimensioned to have aninnermost end that engages and interlocks with said hub and an outermostend supported by said metal shell of said cylindrical body.
 19. Atrefoil structure of claim 18, wherein groups of said leg sections arearranged side-by-side to form a plurality of equally spaced trefoil legsthat extend from said hub to said metal shell.
 20. A trefoil structureof claim 19, wherein each of said leg sections includes a protrusion onone lateral side and a recess on another lateral side, said protrusionand said recess being dimensioned, wherein a protrusion on one legsection is matingly received in a recess in another leg section whenmultiple leg sections are arranged side-by-side to form a trefoil leg.21. A trefoil structure of claim 20, wherein said hub is comprised of aplurality of side-by-side pre-formed refractory hub sections.
 22. Atrefoil structure of claim 21, wherein a hub section is thicker than aleg section, wherein each hub section engages at least two side-by-sideleg sections.
 23. A trefoil structure of claim 18, wherein said legsections are supported by said metal shell by elongated bars attached tosaid metal shell, said bars being received in channels formed in theoutermost ends of said leg sections.
 24. A trefoil structure of claim23, wherein said channels are formed in the edge of said leg sections.25. A trefoil structure of claim 18, wherein shims are disposed betweensaid metal shell and the outermost end of at least one of said legsections.
 26. In a rotary kiln having a refractory lining in the kiln, aheat exchanger assembly, comprised of: a heat exchanger hub comprisingrecesses; multiple heat exchanger legs, each heat exchanger leg havingan inner end received in the recesses of said heat exchanger hub and anouter end installed adjacent said refractory lining, each heat exchangerleg comprised of side-by-side preformed leg sections, each of said legsections being a unitary cast refractory shape that extends between saidheat exchanger hub and said refractory lining, said leg sections beingstacked together along the axial length of the kiln, each of said heatexchanger leg sections having an elongated protrusion on one side of theleg section and an elongated recess on an opposite side of the legsection, said protrusion on a heat exchanger leg section dimensioned tofit in mating fashion within a recess on an adjacent heat exchanger legsection to interlock adjacent heat exchanger leg sections and to preventlateral movement of the adjacent leg sections relative to one another,said protrusion and recess extending along a major portion of the lengthof said elongated leg section in a direction between said inner end andsaid outer end of said leg section.
 27. A rotary kiln as defined inclaim 26, wherein each heat exchanger leg section includes a flared,outer end dimensioned to be positioned along the inner surface of saidkiln.
 28. A rotary kiln as defined in claim 26, wherein each said heatexchanger leg section has an overall length L greater than about three(3) feet.
 29. A rotary kiln as defined in claim 26, wherein each saidheat exchanger leg section has a flared, inner end.
 30. A rotary kiln asdefined in claim 28, wherein said heat exchanger assembly includes aplurality of hub sections, said inner end of said legs interlocking withsaid hub sections.
 31. An elongated, pre-cast leg section for use informing a leg in a heat exchanger in a rotary kiln by stacking aplurality of said leg sections together along the axial length of saidkiln, said leg section having an inner end and an outer end and anelongated protrusion on one side thereof and an elongated recess on anopposite side thereof, said protrusion and said recess being dimensionedsuch that a protrusion on one leg section fits in mating fashion withina recess on an adjacent leg section to interlock said one leg section tosaid adjacent leg section and to prevent lateral movement of theadjacent leg sections relative to one another when said legs are stackedtogether along the axis of said kiln, said protrusion and recessextending along a major portion of the length of said elongated legsection in a direction between said inner end and said outer end of saidleg section.